Photo-electric tube



Dec. 22, 1931. K ZWORYlglN 1,837,744

PHOTO ELECTRIC TUBE Original Filed May 20, 1926 |NvENToR I//ad/m/'r A. ZWOry/f/h ATTORNEY Patented Dec. 22, 1931 UNITED STATES PATENT OFFICE VLADIMIR K. ZWORYKIN, OF SWISSVALE,

PENNSYLVANIA, ASSIGNOR T WESTING- VANIA PHOTO-ELECTRIC l'.PUIBE Application led Hay 20, 1926, Serial No. 110,575. Renewed .Tune 7, 1929.

My invention relates to methods and materials employed in the construction of photo'- electric cells and it has particular reference to the manufacture of photoelectrically active electrodes to be used therein. v

Since the discovery that certain substances would emit electrons when exposed to the action of light, there has been but little improvement in the manufacture of photoelec- ,o tric cells employing metals of the alkali group, such as sodium, potassium, rubidium and caesium as the photoelectrically active material.

In the Physikalische Zeitschrift, No. 15,

August 1911, 12' Jahrgang, Physkialische Zeitschrift XI, 1910, Elster and Geitel de-` scribed a method for the preparation of such cells, which is essentially that in general use today. The steps involved inthis method are substantially as follows:

The cell, which is provided with two electrodes is lirst evacuated. A small amount of potassium is then so distilled from a side container over on the interior of the cell,

that it deposits on the walls in contact with one. of the electrodes. Hydrogen is next admitted, and an electrical discharge is caused to occur between the electrode and the potassium coating. The hydrogen combines chemically with the potassium, producing a substance much more sensitive to light than pure potassium. By heating one portion of the cell, the potassium may be driven oil", leaving a transparent window for the entry of the light to be measured. yIf desired,

grees C.,while caesium, which has not previously been used to any great extent, has a. melting point o'f 25 degrees C.

Because of this danger of redistillatiom the photoelectric cells now in use are made with a complicated eiectrode and press in order to prevent the redistilled metal from bridging the electrodes when in use. Nevertheless, 'they must at all times be handled carefully, and guarded against being overwhereby the desired photoelectric substance may be made on a commercial scale in an inexpensive manner.

A further object of my invention is to provide material for the active electrode of photoelectric device and which is a solid at temperatures in the neighborhood of 100 C.

These ob 'ects I attain in a new and novel manner by ringing together, at the temperature of liquid air, predeterminedl percentages of the photoelectric active material, which has a low melting point, and another element having a much higher melting point and then causing the temperature y to be raised to a point at which the two elements will melt and amalgamate. More specifically, in the preferred form of my invention, I mix with sodium, potassium,

or other active element, a small percentage of barium or other element of the alkaline earth group, having a melting point considerable above that of the said active material. I have found that a particularly sensitive alloy may be made by employing from 90 to 95% of which need not be exceeded in the process of exhausting the' finished device. The melting point of the alloy depends upon the percentage of vbarium,being higher as this percentage'is increased. Too great a proportion of barium is detrimental, however, since the light scnsitivit 'decreases with an increased amount thereo Within the percentages given' the alloy is, forl all practical pur s, ]ust as 'sensitive as metallic potassium a one.

With the foregoing principles in mind, the

. single lfigure of the accompanying drawing shows a photoelectric cell adapted to embody my in vention.' It comprises a glass container 1 having, on its interior wall, a coating 2 of photoelectric material, which is the subject matter of my invention. Sealed through the 4p wall of the tube 1, in a'manner well known in the art, is a cooperating electrode- 3. An inleading wire 4 extends t rough the wall of the tube and makes contact with the coating 2. While a tube of the foregoing character may be employed in connectlon with the. photoelectric substance of my invention, it will-be evident that the latter is not limited to this particular tube structure, but that other forms of enclosing vessel well known in the art will also be suitable.

My preferred method of preparing m new photoelectric substance is as follows: bout 1 or 1.5 grams of pure metallic potassium is further purified by repeated distillation in a vacuum from one section of a glass device to another, the im urities tending to remain in the ortions o the device from which the meta has been driven oi. Approximately .5 grams of barium is next treated in the same manner, the distillation being re eated until 1t is reasonably' certain that o y the pure metal is left. Y

Both the potassium land barium are then chilled to the temperature of liquid air' and are placed together while cold in a receptacle which is carefully exhausted. The temperature is then raised to 400 C., which causes the two elements to unite or amalgamate into a substance or alloy, which, as stated previously, will have a melting point somewhere in the neighborhood of 100 C. A desired portion of this alloyA is then distilled over onto" the interior surface of the tube `in which it is to be employed and the tube permitted to cool down to room temperature.

It is now feasible to exhaust the tube in the usual and well-known manner, with the assurance that none of the photoelectric substance will be undistilled in the finished cell.l

Such portions of the alloy-covered surface which are desired clear ma be heated and the alloy driven oi, as is usua y done when manufacturing photoelectric 'cells according to is the ease with'which a'high vacuum may attained in devices wherein m new allo 1s employed as the photoelectrica y activey e ectrode. No elaborate recautions are necessary to prevent theX alloy rom distilling oi during evacuation nor in the usual course of events will the device become lled with potassium vapor while in use. These advantages are due to the fact that my new alloy has, as before stated, a melting point which is high in comarison to that of the photoelectrically active constituent thereof. I

Since less care is requiredin pre aring devices employing my new alloy, t e cost of manufacturin 1s accordin ly reduced, while the quality o the iinishe product ma kept in all respects equal to, if not be r, than when potassium alone is used.

Numerous other combinations of photoelectrically active elements having low melting points with alloying agents in order to secure a substance having the desired electrical and physical characteristics will suggest themselves to those skilled in the art to-which my invention pertains. Such combinations I consider as fallin within the range of equivalents to which am entitled and my invention is notto be limited except insofar as is reuired by the prior art and the scope of the following claims. I claim as my invention: 1.` A photoelectric substance comprisin an element of the alkaline earth group an an element of the alkali group.

2. A photoelectric substance comprising barium and potassium.

3.v A photoelectric substance comprising an element of the alkaline earth group and' an element of the alkali grou the substance having a melting point o approximately 100 4. A composite material comprising a photo-active element having a melting point below one hundred degrees centigrade and a second element havin a melting point of a proximately six huned degrees centigred; 'n

5. A photoelectric alloy comprising potassium and havin a melting point of approximately one hun red d centigrade.

6. A photoelectric composite material having a melting point above that of a photoelectrically active constituent thereof. f

7. Aphotoelectricmaterialhavingamelt- 189 naam ing point of gproximately one hundred de grees centigr e.

8. The method of preparing a, photoelectric compound which comprises separately distilling the constituent elements m vacuo, chillin the distillates to the temperature of liqf ui air, adding the chilled elements together' in vacuo, and then applying heat. c

9. A. photoelectnc substance comprlsing from. 90% to 95% potassium and from 10% to 5% barium.

In testimonywhereof, I have hereunto subscribed my name this 11th da of Ma 1926.v

VLADIMIR K. Z ORY N. 

